Add hex shape n-grams

[platypii]

Summary

• add a metadata-gated hexadecimal shape projection for UUID and hash-like regexes
• increase ordinary shape windows from 4 to 8 symbols for better date, SSN, phone, and card pruning
• extract ordinary and hexadecimal shapes in one source traversal
• preserve compatibility with indexes that do not contain either shape layer

Performance

On the local 25k-row WildChat sample, the final index is 2.0% larger than the shape-4 index; the hex layer itself adds 0.19% over shape-8. Candidate blocks changed as follows:

• slash date: 151 to 76
• SSN: 1,401 to 6
• phone: 1,401 to 42
• credit card: 1,401 to 14
• UUID: 2,500 to 49

Common dash dates and unseparated 40-character hex strings remain unselective on this corpus.

Verification

• npm test (142 tests)
• npm run lint